In many semiconductor integrated circuits, Group III-Group V compounds (in the periodic table of elements), or III-V compounds, are used to form various electrical devices, such as high power field-effect transistors, high frequency transistors, high electron mobility transistors (HEMTs), or metal-insulator-semiconductor field-effect transistors (MISFETs). One example of III-V compounds used in semiconductor integrated circuits is gallium nitride (GaN). In many applications, the electrical devices are formed on a buffer layer, which is intended to be an undoped III-V compound layer. However, because of the presence of oxygen, silicon, and/or other impurity elements in the processing chamber for forming the buffer layer, the buffer layer usually becomes an unintentionally doped III-V compound layer having N-type doping. Thus, compared with the undoped version, the unintentionally doped buffer layer potentially provides a relatively low resistance path for leakage currents.